Are there any apps for the iPad 4 for converting audio files into MP3?

hi, Not sure if I'm using the correct terminology, or if this has been posted before, I need to convert some of my audio files into mp3, and since I can't find the right app for it I use a free web-based online tool for converting.
but it would be easier for me to have an app on my ipad and save some time.

I would welcome any suggestion from you guys that will help in making decision.
thanks